1. Field of the Invention
This invention relates to motion sensors, and more particularly to sensors of angular velocity for electronic speedometers or the like.
2. Description of the Prior Art
Numerous sensors have been developed for measuring the angular velocity of a rotor. One such sensor depends for operation upon a magnetic field generated by a permanent magnet or an electromagnet. The magnet is positioned so that the lines of flux of the magnetic field pass through a toothed or apertured ferromagnetic part of the rotor. As the rotor turns, the passage of the rotor teeth or apertures through the magnetic field causes flux changes, inducing an alternating current in an associated sensing coil which is proportional to the angular velocity of the rotor. The output of the sensing coil is applied to an auxiliary electronic device, such as an electronic tachometer, to provide some desired function or display.
There are many instances in which a sensing of the angular velocity of a rotor is used to operate more than one electronic device. For example, a truck might be equipped with an electronic speedometer and also an anti-skid system, both of which depend for operation upon a sensing of the angular velocity of the vehicle drive shaft. Typically, if both devices are to function at the same time, two different sensors would be used which are each separately coupled to the same rotor. Using a single conventional sensor coil would be impractical because the usual multiple electronic devices used in such a situation are usually sufficiently sensitive that they would interfere with each other. There is a need for a means to obtain electrically isolated outputs from a single sensor associated with a rotor or the like, and particularly from a single sensor occupying no more physical space or different mechanical mounting arrangement than the conventional single sensors presently in use.
Many patents disclose two coils either coaxially wound or positioned in juxtaposition to one another. Indeed, such an arrangement of two coils is elementary to the functioning of a transformer. Typical of these patents are: U.S. Pat. No. 3,510,858, issued to Flanagan on May 5, 1970; U.S. Pat. No. 3,586,964, issued to Strauch on June 22, 1971; U.S. Pat. No. 3,882,436, issued to Chass on May 6, 1975; U.S. Pat. No. 4,035,751, issued to Walthew on July 12, 1977; and U.S. Pat. No. 4,097,756, issued to Gee on June 27, 1978. Each of these patents discloses a pair of coils designed to interact with each other, either through coupled fields, as in a transformer, or through direct electrical inter-connection of the coils. None of these patents discloses a sensor adapted for association with a single rotor and characterized by outputs isolated from each other but each separately indicative of the rotor revolutions.